1. Field of the Invention
The present invention relates generally to a phase compressor which phase-compresses a phase modulated signal, and is directed more particularly to a phase compressor which compresses the phase of a signal with a large phase modulation angle and then supplies the phase compressed signal to a phase detector.
2. Description of the Prior Art
There are existing phase detectors that have a limitation such that the phase modulation angle .theta. of the phase modulated signal must be - .pi./2 &lt; .theta. &lt; .pi./2. This limits the sensitivity of modulation and hence the sensitivity of detection. Limiting the maximum value of the phase modulation angle .theta. also limits the modulation index and makes it difficult to obtain a good signal-noise ratio.
To avoid this limitation, it has been proposed that the phase of the reference carrier signal used for phase detection be shifted by a predetermined angle before this phase-shifted reference carrier signal is added to a phase modulated signal (for example, a phase modulated television signal). The phase of the resultant signal is compared with the reference carrier signal, and satisfactory phase demodulation is possible, even if the phase of the modulated signal is varied by an angle greater than + .pi./2 and smaller than - .pi./2. That type of the phase demodulator is disclosed in U.S. patent application Ser. No. 519,028 filed Oct. 29, 1974, now U.S. Pat. No. 3,949,314 and assigned to the same assignee as the present application. The phase demodulator of that application can demodulate a signal that has its phase modulated by an angle .vertline..theta..vertline.&gt; .pi./2, but the circuit is still limited to demodulating signals phase-modulated by an angle .vertline..theta..vertline.&lt;.pi..